The present invention relates to a device for extruding honeycomb structures which are used as catalyst supports, heat exchangers or filters.
Conventionally, the mechanical strength of the whole of the ceramic honeycomb structure or of the outer peripheral portion thereof has been improved by forming an outer wall B which is thicker than a grid-shaped wall A, in the outer periphery of the honeycomb structure as shown in FIG. 1.
For extruding such a honeycomb structure as described above, devices as shown in FIGS. 2 and 3 are conventionally used. These devices are provided with a die mask 1 having an inner surface 31 of a smaller diameter than an extrusion die 3, in the outer periphery of the outlet side of the extrusion die 3 disposed within a cylinder 2 respectively.
The extrudable material which was supplied from the cylinder 2 passes feed passageways 4 and grid-shaped extrusion slots 5 which are formed within the die 3, under pressure to be extruded therefrom.
Then, the extruded body is formed by the inner wall 31 of the die mask 1 into a predetermined outer form and the thick outer wall is also formed.
However, according to the device of FIG. 2, the material is pressed by the tapered inner wall 31 of the die mask 1 toward the center thereof after being extruded out of the die 3. Therefore, distortion is easy to occur in the connecting portion C between the grid-shaped wall A and the outer wall B of the obtained honeycomb structure as shown in FIG. 4. As a result, the mechanical strength of the connecting portion C is decreased.
And in the device of FIG. 3, the die mask 1 which is contacted with the die 3 is provided with an opening portion 30 in the whole circumference of the inner wall 31 thereof. In the outer periphery of the obtained product, the thick outer wall is formed by the material which is supplied from the extrusion slots of the outer peripheral portion of the die 3 through the opening portion 30.
However, according to the device of FIG. 3, since the connecting portion C shown in FIG. 4 is crushed by the material supplied to the outer periphery of the extruded body, distortion is easy to occur therein.
Accordingly, one object of the present invention is to provide an extrusion device for producing honeycomb structure having an excellent mechanical strength.
Another object of the present invention is to provide an extrusion device for producing honeycomb structures provided with a thick outer wall respectively without producing any distortion in the grid-shaped wall surrounding a large number of open passages.
Still another object of the present invention is to provide an extrusion device for producing honeycomb structures of which outer peripheral surface is smooth.
Further object of the present invention is to provide an extrusion device for producing honeycomb structures having an excellent thermal shock resistance.